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Poster: Headphone Date: May 31, 2011 10:42pm
Forum: GratefulDead Subject: Tech: Pitch correction

I'm hoping to get advice on pitch-correcting some old tapes where the batteries in the recorder were slowly dying during a show. I see a lot of thanks to Joe B. Jones for his work in this regard, but of course anyone can suggest links to read, etc. Thanks a lot.

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Poster: dead-head_Monte Date: Jun 1, 2011 8:08pm
Forum: GratefulDead Subject: Re: Tech: Pitch correction

Pitch Correction & Speed Correction

• CM has done numerous pitch correction upgrades recently based upon the pitch & speed error information supplied by Joe B. Jones. Apparently, Joe has perfect pitch. Perfect pitch analysis is the best way to go to get your error parameters defined accurately.

There are numerous Audio s/w products being used to correct Pitch and/or Tape Speed errors on recordings. You can correct the Pitch only, the Speed only, or both Pitch and Speed (Resample Mode). It is imperative to understand this. I have some limited experience and knowledge to share with you. Listed below are some "ptich correction" conversations you can read and learn from.

Phil Lesh on trumpet playing Jazz tapes - my pitch & dehiss upgrade for Phil's 70th birthday

Are these tapes in tune?

audio restoration software discussion

pitch correction module in Samplitude Pro s/w
dead-head_Monte-samplitude-pitch-speed.jpg?cnt=0



This post was modified by dead-head_Monte on 2011-06-02 03:08:56

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Poster: Headphone Date: Jun 1, 2011 10:26am
Forum: GratefulDead Subject: Re: Tech: Pitch correction

Thanks Monte, that's helpful. I think my big problem is correcting the pitch that is changing over the course of an hour or two. Love to hear from someone who has done that.

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Poster: dead-head_Monte Date: Jun 2, 2011 11:40am
Forum: GratefulDead Subject: Re: Tech: Pitch correction thesis

Computer Animation Models vs Pitch Correction Models

Animation Fairings and Pitch-correction Algorithms —

Fairings, also known as ease-ins /outs, slow ins / outs... whatever you want to call them, are what you need in your audio Restoration software! Fairings are about interpolation - or in plain English, how you either accelerate or decelerate from one key frame of animation (or segment of Audio) to the next.

Take a simple example of animation: suppose we want to animate a scene in which a car begins a journey. First the car is at rest, then a few seconds later it will be up to speed. But it does not go instantly from one state to another; it will accelerate from being static to its cruising speed. This acceleration is one kind of fairing.

The ink and paint program Animo deals with fairings very comprehensively. The author of the "Animation Fairing doc" I linked to has grabbed these screen shots from it to illustrate things. Here is how you represent a linear move between two key frames in Animo and it shows a case where there are no fairings:

animation graph showing linear move

The starting frame is at the bottom left and the end frame (in this case, frame 16) is at the top right. As you move across the graph from left to right, you are progressing in time. As you move up the graph, you are altering a value. This value will very often be the distance of a movement, but it can just as easily be a change in a quality such as color or degree of blur and so on. In your case, it's tape speed error and the resulting pitch error. By the way, if the line of the graph were horizontal, this value would be the same and this would then in effect be the same as a hold.

In the present case, the graph above shows the movement of our car when it is up to speed and travelling at a constant rate. During these frames, therefore, there are no fairings.

A linear move, as is obvious from the graph above, means that for every frame, every in-between change is the same amount. This means that each frame (the "fence" at the bottom) is equidistant from its neighbor.

Many movements start slowly, get up to speed, then end slowly (for example, if a character turns their head, the move might well start and end with fairings like this:)

animation graph showing fairings in and out of a move

On the other hand, many movements may accelerate from scratch but end suddenly without a fairing. For example, suppose you are animating a hammer hitting a nail. The hammer will move by accelerating until the point at which it hits and it stops dead. For this very common sort of move, you want a curve like this:

animation graph showing fairing in only - acceleration

The opposite would be a move that only slows. (Say a marble rolls to a halt; it will decelerate throughout the move):

animation graph showing fairing out only - deceleration.

Note two things about these graphs: first, each control point has a handle with which the animator can "finesse" the move to their heart's content by adjusting the slope of the curve. Second, though not shown here, it is also possible in Animo to add as many extra control points as you want to make very much more complex movements such as oscillations.

The examples above are just basic curves. By altering these curves carefully, a piece of average animation can be given the extra sparkle and flair that makes it special. For instance, by changing the direction of a fairing's curve, you can create an "overshoot" in the animation. Learning how to tweak these fairings is the mark of a good animator.

Fairings are always used by character animators who are professional. Basically, we have three types of motion: slow-fast-slow; fast-slow-fast; and linear (steady drip, drip, drip...). Animation motion sequences also include halts or pauses (periods of no motion).

In your case, your recording speeds became slow, and then became slower, and more slower. Audio pitch is always affected by recording speed errors. Was your recording speed problem caused by your batteries discharging below the "specified voltage level"? Recording speed slowness errors can be caused by a tape recorder's battery voltage dips. In the old days, you'd have to pitch-correct your bad recordings by slowing down their playbacks. They had to be played on tape decks with capstan speed over-ride controls. Using Restoration software today, you can digitally do this by increasing the Resampling factors faster and faster, by the exact inverse amount. This is what you're describing. Read the Tape Transports technical description by Monte.

What about getting your tapes and recordings transferred "correctly", and the pitch is already bad on tape - because it was recorded this way? Make sure your reels [or recordings] are "played back correctly" by using professional equipment and devices. This guarantees playback speeds are reliable. REMEMBER, the "normal transfer speeds" will cause your errors to have a pitch that gets fast, faster, and more faster in your case. You'll have to digitally slow it down, more and more, as you go down the digital tracks in the list.

If you wanted to use Samplitude AND "Audio animation" for pitch-correcting this, one approach is to get a software design engineer to design a Keyframe Editor for you that features spline-based smoothing. This means adding and placing new points on the time line. Each point has Bezier control handles. Allow the Pitch Correction Artist to edit his/her fairings this way. The engineer can write a software programming algorithm and script for this, and port that new programming script into Samplitude's Resampling / Time Stretching / Pitch Shifting Module. Samplitude Product Managers should integrate this "NEW revision & upgrade" by incorporating it into a redesigned Control Panel that includes the added features, adjustments, and controls.

Customizing the Keyframe Graph Area in the Timeline

Video Editing Techniques - keyframes

dead-head_Monte-samplitude-pitch-speed.jpg

For now, Samplitude's interpolation is always using the "linear motion" model (steady drip, drip, drip) - correcting the speed and pitch for you this way.

In the meantime, you can manually correct your tapes like this. Use a "least common denominator" guestimation method. Try this. Find the longest segments (keyframes) of tape material you can keep correcting perfectly using s/w interpolation - without over-shooting or under-shooting the Resampling methods you try using. Check the playback for each experiment you run. Does it sound correct yet? Are these keyframe segments about 10 minutes long, 5 minutes long, or about 1 minute long?

If you can do Resampling correction to 90 minutes of your material in 10-minute segments, it will take you 9 times to repeat this process: measure the pitch error; set up the speed-correction algorithm in Samplitude (or some other Restoration s/w); mark the in & out points for the first 9-minute segment; apply the correction. Repeat the audio segment marking process 8 more times, going down the length of tape, and apply the correction each time, using Resampling mode. That's several hours of work. If you tried one-minute pieces, done manually this way, it will take a day or two. My advice is to always go back and check your work for mistakes. Be especially cautious and careful when you're doing very mundane repeat-tasks like this.

Whatever you try in your experiments, make sure you test a sample from the start of the tape, test a sample at 25% into the tape, test a sample at 50% into the tape, test a sample at 75% into the tape, and test a sample near the end of the tape. This is the correct way to sample the entire tape in any evaluations you may wish to correlate. This is the best way to experiment. Probably in your case you'll need to increase the amount of pitch correction more and more as you move further down the tape on your defective reels.


• Monte Barry has worked with numerous computer animation systems as a video engineer
- video engineer for Computer Image Productions, Denver, CO, 1984 to 1986

Scanimate computer animation system used analog video processing
designed and built by Computer Image Corporation in Denver

Asheville1.jpg

- see the Scanimate alumni web page
- watch their
Dream Machine movie trailer on YouTube - 01:38 length

• 20 years ago, I was running Autodesk's 3D Studio animation s/w on my PC

"News Update" smoke and mirrors demo image by Monte in 1991
designed and rendered on my PC in 3D Studio ver 2.0 DOS

update.jpg

Monte's Taper Handbook



This post was modified by dead-head_Monte on 2011-06-02 18:40:13

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Poster: Headphone Date: Jun 1, 2011 7:40pm
Forum: GratefulDead Subject: Re: Tech: Pitch correction thesis

All very amazing! My head is (happily) spinning!

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Poster: dead-head_Monte Date: Jun 2, 2011 9:51am
Forum: GratefulDead Subject: Re: Tech: "Flying Faders" same thing as "Flying Reels"

Flying Faders automation sequences shown on Neve's VR Audio Mixer

default.jpgThis Flying Faders demo on YouTube is showing you several animation sequences. They have been strung together into one automation control file. These simple demo file(s) are created quickly and easily by the Sound Engineer in The Studio. The automation control file is being played back to control the faders on the soundboard mixer. We have a variety of motion types in this very simple automation sequence.

In short, it's the same thing as if the Sound Engineer in this demo is also being a Character Animator. He designed a "cartoon movie" and played it back on the Flying Faders!

• I'm suggesting it's the exact same thing for many Pitch Correction errors. Samplitude Product Managers should allow Pitch Correction Artists to edit Key Frames, and Create & Modify Fairings, just like Character Animators do. That's exactly what Neve and other pro-Audio outfits have been doing for decades. Sound Engineers designing Flying Fader profiles are doing the same things that Character Animators are doing when they make cartoons.

In my thesis, I'm saying it's the same thing as if the Sound Engineer is also being a Pitch Correction Artist, and a Character Animator. He needs to be able to design a "cartoon movie" and play it back on the Flying Tape Deck Reels!

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Poster: dead-head_Monte Date: Jun 2, 2011 10:23am
Forum: GratefulDead Subject: Re: Tech: 'Flying Faders' same thing as 'Flying Reels'

Fastrack Hybrid Controller - an overview from Editware

Fastrack - The True Hybrid Controller

This Fastrack demo on YouTube is showing you a Linear / Non-linear editor and controller. Notice their design interface. It's an extremely simple and very powerful hybrid. Fastrack has control of tape decks, audio and video servers, mixers, switchers, and other controllable devices.

Time Tailor Post - Real Time Reduction explains The Fastrack features in more detail. Yes, it's super-overkill for you.

It demonstrates to Samplitude Product Managers what professionals have been doing for decades.

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Poster: dead-head_Monte Date: Jun 1, 2011 10:44am
Forum: GratefulDead Subject: Re: Tech: Pitch correction

Tape Speed Slewing